1. Field of the Invention
This invention relates generally to a tear tape for use with hermetically sealed plastic packages.
2. Background Art
Plastic packages for perishable food products require a hermetic seal in order to preserve the food products during shipment and storage. It is also desirable to provide a tear tape or tear strip on such packages to allow a person to open the package easily. Using a tear tape to open a package also provides a clean tear along an edge of the package. This is especially useful so that a package can be easily reclosed with a zipper. Such a tear tape must not affect the initial hermetic seal of the package.
A drawback with current tear tapes is that they do not seal well with plastic packaging and therefore do not provide a good hermetic seal at the sides of the package which are likely heat sealed together. A conventional tear tape often is applied with pressure sensitive adhesive. While pressure sensitive adhesive adheres well to packaging, it does not provide a true hermetic seal, which is achieved with a heat sealable tear tape.
One known tear tape uses linear low density polyethylene (LLDPE) as a heat sealable adhesive. The melt temperature of LLDPE, which is the temperature required to activate the heat seal between the tear tape and the package film, is approximately between 220xc2x0-230xc2x0 F. Applying enough heat to reach the melt temperature of LLDPE can cause distortion of the package film. Additionally, because it takes time to heat the LLDPE sealant layer of the tear tape to these temperatures, the speed of processing products containing such a tear tape is limited.
Furthermore, current tear tapes are unreliable when used on packages that are exposed to high humidity and refrigerated conditions. Such tear tapes can become brittle and break when pulled to open the package. Additionally, currently known tear tapes have heat resistance limitations and demonstrate heat shrinkage if the packaging machine or manufacturing line which affixes the tear tape onto a package is shut down for any length of time.
The tear tapes of the present invention have a polymer sealant layer which has a melt temperature of below approximately 220xc2x0 F. Accordingly, the speed at which the tear tapes can be applied and sealed to packaging films can be increased because it takes less time to heat the polymer sealant of the tear tapes to the melt temperature. Additionally, by using a polymer sealant having a melt temperature of below approximately 220xc2x0 F., distortion of packaging films is greatly reduced because the packaging films are subjected to lower temperatures when tear tapes are applied and sealed to the packaging films.
It is one of the principal objectives of the present invention to provide tear tapes that can be used on hermetically sealed packaging while not affecting the hermetic seal of the package.
It is another object of the invention to provide tear tapes that seal to plastic packaging at temperatures below approximately 220xc2x0 F. and will not cause distortion of the package film.
It is still another object of the invention to provide tear tapes that can be applied to a package at high speeds.
It is another object of the invention to provide tear tape structures which have high heat resistance.
It is another object of the present invention to provide heat resistant tear tape structures that are based on oriented polyethylene terephthalate (PET), oriented polypropylene (OPP) or biaxially oriented nylon (BON).
It is still another object of the invention to provide heat sealable tear tape structures which do not demonstrate tape breakdown or shrinkage if the manufacturing line is shut down for long periods of time.
It is a further object of the invention to provide heat resistant, heat sealable tear tapes that have a high resistance to moisture.
It is still a further object of the invention to provide reclosable packaging having initial hermetic seals and heat resistant, heat sealable tear tapes.
It is another object of the invention to provide tear tapes that maintain strength when exposed to refrigerated conditions.